Liquid level indicator system

ABSTRACT

A liquid level indicator system in which a liquid in a tank raises or lowers a float containing angularly positioned magnetic elements according to the level of the liquid present in the tank. The float is co-axially positioned about a vertical tube containing a plurality of reed switches longitudinally aligned and connected in parallel. The magnetic element of the float closes the reed switches at or near the level at which the float is located, thereby short circuiting resistances in an electrical circuit in proportion to the amount of liquid present in the tank. The electric current in the circuit operates a liquid level indicator gauge.

United States Patent DiNoia et al. 1451 July 25, 1972 [54] LIQUID LEVELINDICATOR SYSTEM 2,411,712 11/1946 De Giers ..73/313 [72] Inventors:Emanuel D'Noh, Brim Cliff Manor 3,408,053 10/1968 Vantroba...-. ..73/313X N Theodore R Breunlch Stamford 3,293,579 12/1966 Harper ....200/84 C X6 2,771,774 11/1956 Fomasieri ..73/313 [73] Assignee: Universal 011Products Company, Des Primary Examiner-Louis R. Prince Flames, AssistantExaminer-Daniel M. Yasich [22] Filed: 13, 1970 Attorney-James R.Hoatson, Jr. and Philip T. Liggett 1 1 pp 63.348 57 ABSTRACT A liquidlevel indicator system in which a liquid in a tank [52] US. Cl ..73/3l3,73/D1G. 5, 200/84 C raises or lowers a fl containing angularlypositioned [51] Cl. ..G0l123/12 netic demems according t the level ofthe liquid present in [58] Field o1'Search ..73/3l3,D1G. 5; 33/126.7R;the tank The float is comxiany positioned about a venical Zoo/84C tubecontaining a plurality of reed switches longitudinally aligned andconnected in parallel. The magnetic element of [56] References cued thefloat closes the reed switches at or near the level at which UNITEDSTATES PATENTS the float is located, thereby short circuitingresistances in an electrical circuit in proportion to the amount ofliquid present LCVHlS 73/3 1 3 in the tank The electric current in thecircuit operates a 1,617,287 2/1927 Huggins ..73/290 DIG. 5 levelindicator gauge. 2,927,176 3/1960 Au1d,. lr. et a1. ..73/290 2,764,2949/1956 Johnson ..33/126.7 R 8 Claims, 7 Drawing Figures $4 i l l i 5 $346 5 l i ii 1 R2 E i /60 i I; 43 E 'i l 4/ Q I R/ /0 l I v I I s s2 2aI: Z

i I ,1 as 1'} LA I :1 42 1 11 i 1' 37 1 39 1 2 I i i 1 26 :1 {1 1 L i a5-30 z /35 l f atented July 25, 1972 4 Sheets-Sheet 1 LIQUID LEVELINDICATOR SYSTEM This invention relates to a liquid level indicatorsystem in which a liquid in a tank raises or lowers a float according tothe level of liquid present. The float contains a magnetic element andis co-axially positioned about a vertical tube containing a reed switchcircuit. The magnetic element of the float closes reed switches at ornear the level at which the float is located, thereby short circuitingresistances in an electric circuit in proportion to the amount of liquidpresent in the tank. The current in the electric circuit operates aliquid level indicator gauge.

ln existing liquid level indicator systems utilizing reed switches, asingle reed switch is used within a hollow vertical tube and single ormultiple ring magnets are used as magnetic elements. Because of therelatively short length over which a ring magnetic can influence theelectrical condition of a reed switch, the existing liquid levelindicator systems are useful only for measuring liquid level inrelatively shallow tanks and for the purpose of indicating when a liquidlevel passes a predetermined point, such as an empty or dangerously lowliquid level in a liquid storage tank.

Furthermore, since the present level indicating systems having a reedswitch utilize magnetic rings or other magnetic elements that set up auniform magnetic field, the reed switch undergoes numerous changes inelectrical condition as the tank in which it is utilized is emptied orfilled. In these present indicator systems, as the float movesvertically to traverse the length of the reed switch, the reed switchundergoes five different changes in electrical condition. When the floatcontaining the magnetic element is distant from the reed switch, theswitch is an open condition. As the magnetic element approaches the endof the reed switch, the switch is closed. The switch opens again whenthe magnetic element is moved slightly closer toward the center of thereed switch, but closes again when the magnetic element is opposite thecenter of the reed switch. As the magnetic element moves away from thecenter of the switch, the reed switch opens until the element isapproximately opposite the other end of the reed switch, at which pointthe switch is closed. As the magnetic element moves further away fromthe reed switch, the reed switch once again is opened. This repeatedchange of condition of the reed switch necessitates an elaborateelectrical circuit to make the switch condition meaningful.

To obviate this problem, plural magnetic rings are sometimes positionedon the float so that the magnetic rings may interact and the resultantmagnetic field will be such as to eliminate the number of switch pointsor control points at which the reed switch is actuated during thelongitudinal movement of the float with respect to the reed switch. Sucha float construction reduces the accuracy of the instrument, however,because of the relatively long longitudinal actuating magnetic field setup by the combination of magnetic rings.

it is an object of the present invention to increase the accuracy of aliquid level indicator system operated by a change in electricalcondition of a reed switch that is activated by a float containing amagnetic element. This accuracy is achieved by reducing the longitudinalor axial length along the vertical tube within which the magnetic fieldis strong enough to actuate a reed switch. Due to one unique aspect ofthis invention, this reduction in influence of the magnetic field isachieved without introducing multiple switch or contact points into thesystem. Such multiple'contact points would cause the reed switch torepeatedly reverse electrical condition, as occurs in conventionalsystems utilizing a single ring magnet co-axially surrounding a verticaltube and moving longitudinally with respect to a reed switch. Thepresent invention solves the problems of inaccuracy and instabilitythrough the unique construction and positioning of a magnetic element toachieve an unsymmetrical magnetic field. The magnetic element of thisinvention is partially in the upper portion and partially in the lowerportion of the float. The moment of inertia about the axis of the innervertical tube of the part of the magnetic element in one of the portionsof the float is larger than the moment of inertia of the part of themagnetic element in the other portion of the float. The part of themagnetic element having the greater moment of inertia may be positionedin either the upper or lower portion of the float, as may the part ofthe magnetic element having the smaller moment of inertia. The innervertical tube contains at least one longitudinally positioned reedswitch. The float is co-axially positioned about and vertically movablewith respect to the inner vertical tube in response to the liquid levelwithin a tank. As a result of this construction, the magnetic elementexerts a stronger magnetic field at the axis of the inner tube at thatportion of the float wherein the moment of inertia of the part of themagnetic element is small when compared with the magnetic field at theaxis at that portion of the float where the moment of inertia is large.That is, constructed and positioned in accordance with this invention,the magnetic element will produce a magnetic field stronger toward oneend of the inner vertical tube than toward the other end of the innervertical tube at the axis of the inner tube. This feature of theinvention both increases the accuracy of the level indicator system byreducing the axial influence of the magnetic field, and eliminates theoccurrence of multiple closure points in the operation of the reedswitch.

Another object of the invention is the utilization of a liquid levelindicator system containing a reed switch circuit actuated by a risingor falling float for use in measuring incremental changes in the liquidlevel over a substantial depth. Previously, the depth over whichmeasurements could be taken was limited to just more than the length ofa reed switch, with the increments of measurement being the distancebetween the five closure points previously described. Utilizing anotheraspect of the present invention, the length over which incrementalmeasurement is possible is increased by the longitudinal alignment of aplurality of reed switches connected in parallel with each other withina vertical tube. A plurality of electrical resistors are connected inseries with each other to form a resistor string which is one of thecommon terminals by means of which the reed switches are connected inparallel. That is, each of the resistors is connected between twoadjacent reed switches to form this common terminal. Each of the reedswitches is consecutively actuated and deactuated by a falling floatlevel or by a rising float level in a tank containing a liquid.Actuation of each of the reed switches short circuits a specificresistor or resistors, thereby decreasing the overall load in the reedswitch circuit and increasing the electrical current flowing in thatcircuit. The converse is true where the float moves in the reversedirection. The vertical spacing of the adjacent reed switches determinesthe accuracy of the level indicator system. The use of a plurality oflongitudinally aligned reed switches also eliminates the necessity formultiple contact points presently required to obtain any incrementallevel indications in a level indicator system utilizing a single reedswitch.

Yet another object of the invention is to eliminate resonant vibrationof the transmitter or sensing unit of the liquid level indicator system.Resonant vibration is of particular concern because of the longer lengthof the sensing unit made possible by longitudinal positioning of thereed switches. Resonant vibration frequently occurs in fast movingairborne or land vehicles. The source vibration is set up from theinternal mechanical parts of the vehicle or by air or wind resistanceacting on the vehicle, or by a combination of both. Resonant vibrationin the basic transmitter or sensing portion of the liquid levelindicator sYstem is eliminated by fastening an outer guide tube in aparticular manner to the basic inner tube containing a reed switchcircuit and about which a float containing a magnetic element isco-axially positioned. When the inner tube stands vertically by itself,there is a strong tendency for an externalvibration to cause the freeend of the relatively long columnar tube to whip back and forth withinthe liquid or surrounding atmosphere and eventually break off when thefatigue limit of the inner tube structure is reached. This repeatedflexing of the sensing element of the level indicator system can bealmost entirely eliminated by prohibiting the sensing element fromachieving resonant vibration. This is accomplished by positioning theouter guide tube co-axially about the inner tube and firmly attachingthe inner and outer tubes together at their mutually adjacent free ends.The opposite end, or fixed end of the inner tube is rigidly fastened toa support and the outer tube is held in compression against the supportby the inner tube, thereby causing the inner tube to remain in tension.The free end of the sensing element of this structure, when subjected tovibration which at first tends to be resonant, starts to oscillate inresonant vibration. However, the first movement of the free end of thestructure in a cycle of oscillation will cause one portion of the outerguide tube to lift away from the support against which it is compressedin the static condition. This shift in position of the outer guide tubefrom the support changes the magnitude and direction of forces acting onthe free end of the inner tube and thereby dampens the oscillatorymovement at the free end of the sensing element. The free end of thesensing element can never fall into a pattern of resonant vibrationbecause the variable forces acting on the free end cause the resonantfrequency of the sensing element to continually change each time thefree end of the sensing element begins to oscillate.

Still another object of this invention is to increase the accuracy ofthe reed switch circuit by eliminating the presence of stray metallicparticles from the vicinity of any reed switch. In conventional liquidlevel indicator systems utilizing a reed switch, metallic particles leftfrom welds, unfinished edges of a metal tank, and metallic impurities inthe liquid in the tank, tend to alter the normal pattern of actuation ofthe reed switch and thereby distort the liquid level reading. Suchdeviations occur because the stray metallic particles are drawn to themagnetic element of the float, become magnetized, and extend theinfluence of the magnetic field of the magnetic element. To eliminatethe distortions in reed switch operation in this invention, an outerguide tube is positioned radially exteriorly from the float and co-axialwith respect to the inner vertical tube containing the reed switchcircuit. Upper and lower flow ducts connect the enclosure formed betweenthe inner and outer tubes to the exterior of the outer tube. The lowerflow ducts are located or extend below the lower extremity of the floatwhen it is in its lowest float position, while upper flow ducts arelocated or extend above the upper extremity of the float in the upperfloat position. A scavenger magnet is positioned between the float andthe lower extremities of the lower flow ducts. Magnetized particlescarried by liquid through the lower flow ducts into the enclosure formedbetween the inner and outer tubes are disentrained and trapped by thescavenger magnet as the liquid passes through the lower flow ducts. As aresult, the presence of stray metallic particles in the vicinity of thereed switch circuit is eliminated, since there is practically never anyflow of liquid through the upper ducts into the enclosure formed betweenthe inner and outer tubes.

One further object of this invention is to produce a liquid levelindicator system easily adaptable for use with oddly shaped tanks ortanks having a variable cross-section. The same indicator or displaysystem may be used with any liquid storage tank, regardless of theshape, through a proper choice of the resistors positioned betweenadjacent reed switches in the longitudinally aligned plurality of reedswitches. That is, at the vertical level of the sensing element at whichthe liquid storage tank has a large horizontal cross-sectional area, theadjacent reed switches will have positioned therebetween resistorshaving a large electrical resistance. .This is done so that there willbe a large current change in the reed switch circuit by actuation ordeactuation of one of the switches at this level.

This large current change corresponds to the relatively large volumedifferential due to the large cross-sectional area of the storage tankat this level. Conversely, at vertical locations along the sensingelement where the liquid storage tank has a relatively small horizontalcross-sectional area, adjacent reed switches will have a resistor orresistors of small electrical resistance connected therebetween. Thepresence of these smaller resistors in the reed switch circuit asgoverned by actuation or deactuation of one of the reed switches willreflect only a small current differential corresponding to the smallvolume change in the tank due to the relatively small crosssectionalarea of the tank at that level.

The liquid level indicator system of this invention has a variety ofuses and may be utilized to measure the liquid level in fuel tanks,crank cases, railroad cars, ballast tanks, vats, water reservoirs, andvirtually any other liquid storage tank. In addition, the liquid levelindicator system of this invention may also be used to determine theliquid level in compartments subject to flooding, such as compartmentsin a ship, basements of low lying buildings, and mines.

in one broad aspect, this invention is, in a liquid level indicatorsystem having a hermetically sealed inner vertical tube of uniformcross-section constructed of a non-magnetic material; a float carrying amagnetic element positioned coaxially about said inner tube andvertically movable with respect to said inner tube between an upper anda lower float position; and an indicator system having an electriccurrent indicator means and electric power leads, the improvementcomprising: a plurality of reed switches connected in parallel andconnected to said electric power leads and longitudinally aligned withinsaid inner tube; and a plurality of electrical resistors connected inseries with each other and connected to said electric power leads witheach of said resistors connected between two adjacent reed switches.

In another sense, the invention may be considered as, in a liquid levelindicator system having a hermetically sealed inner vertical tubecontaining a reed switch circuit and mounted in a tank containing aliquid, a liquid level display device electrically connected to saidreed switch circuit, a float carrying a magnetic element positionedco-axially about said inner tube and vertically movable with respect tosaid inner tube between an upper and a lower float position, an outerguide tube co-axially positioned with respect to said inner verticaltube, thereby forming an enclosure between said inner and outer tubes,upper flow ducts and lower flow ducts located below said lower floatposition connecting said enclosure to the exterior of said outer tube,the improvement comprising a scavenger magnet positioned verticallybetween said lower float position and said lower flow ducts andlaterally between said inner tube and said outer tube, wherebymagnetizable particles in said liquid are disentrained and trapped bysaid scavenger magnet as liquid passes through said lower flow ducts.

Still another broad aspect of the invention is, in a liquid levelindicating system having a hermetically sealed inner vertical tubecontaining a reed switch circuit rigidly mounted on a support in a tankcontaining a liquid, a liquid level display device electricallyconnected to said reed switch circuit, a float carrying a magneticelement positioned coaxially about said inner tube and verticallymovable with respect to said inner tube, an outer guide tube co-axiallypositioned with respect to said inner vertical tube, thereby forming anenclosure between said inner and outer tubes, and upper and lower flowducts connecting said enclosure to the exterior of said outer tube, theimprovement comprising a firm attachment of said outer tube and saidinner tube at mutually adjacent ends remote from said support, and saidouter tube is held in compression against said support by said innertube, thereby causing said inner tube to remain in tension.

In a final aspect, the invention may also be considered as, in a liquidlevel indicating system having a hermetically sealed inner vertical tubecontaining a reed switch circuit and having first and second ends andmounted in a tank containing a liquid, a liquid level display deviceelectrically connected to said reed switch circuit, a float having upperand lower portions carrying a magnetic element and positioned co-axiallyabout said inner tube and vertically movable with respect to said innertube between an upper and a lower float position, the improvementcomprising positioning said magnetic element partially in said upperportion and partially in said lower portion of said float, and saidmagnetic element is constructed having the moment of inertia about theaxis of said inner tube of the part of said magnetic element in one ofsaid portions of said float larger than the moment of inertia of thepart of said magnetic element in the other of said portions of saidfloat, whereby the magnetic field of said magnetic element is strongertoward one of said first and second ends than toward the other of saidfirst and second ends of said inner vertical tube.

This invention is more clearly illustrated by reference to theaccompanying drawings.

FIG. 1 is an elevational view in partial section of a preferredembodiment of this invention.

' FIG. 2 is a schematic diagram of the electrical circuitry of theembodiment of FIG. 1.

FIG. 3 is an isolated elevational view of the float of the embodiment ofFIG. 1.

FIG. 4 is a plan view of FIG. 3.

FIG. 5 is a sectional view taken along the lines 5-5 of FIG. 3.

FIG. 6 is a sectional view taken along the lines 6-6 of FIG. 3.

FIG. 7 is a schematic diagram of the electrical circuitry of a modifiedform of the embodiment of FIG. 1.

Referring now to FIG. 1, there is shown a liquid level indicator systemcomprised of a sensing element or transmitter 60 and a receivingelement, display device, or indicator system 7.* The major componentparts of the transmitter 60 are the inner vertical tube 2, the reedswitches S1 through S7 the electrical resistors R1 through R6, the float5, and the outer guide tube 10.

Inner vertical tube 2 is mounted on a solid support 1, which may beconsidered to be the bottom of a liquid storage tank. Machine screws 24pass through the tank bottom or support 1 and firmly attach mountingblock 31 to support 1. The mounting block 31 is sealed to support 1 bymeans of an -ring 61. A plug 33 is force fitted into inner tube 2 withan exteriorally threaded portion of plug 33 protruding from inner tube2. Counter sunken screws 23 further attach plug 33 to inner tube 2. Thecenter of plug 33 is filled with a core 34 made of a sealing substance,such as tar, to surround wires 26 and 27 and insure a fluid tight sealat the lower end of inner tube 2. The threaded end of plug 33 isthreadably engaged to interiorally threaded end fitting 62. End fitting62 isforce fitted into an aperture in steel mounting block 31 and isfurther sealed to mounting block 31 by means of an Oring 32. A leakproofseal is thereby formed between the exterior of the inner tube 2 and theexterior of the floor l of the liquid storage tank.

Outer guide tube 10 is positioned radially exteriorly from float andco-axial with respect to inner vertical tube 2, thereby forming anenclosure 13 between inner tube 2 and outer tube 10. Upper flow ducts 12and lower flow ducts 11 connect the enclosure 13 to the exterior of theouter tube 10. The lower extremities of the lower flow ducts 11 extendbelow the lower extremity of float 5 when it is in the lowest floatposition, designated by the numeral 36. Outer tube is constructed withan end cap 18 perforated by upper flow ducts 12. The upper end of innervertical tube 2 is sealed by an end plug 19 having an axial upwardextending threaded stud 17. The end cap 18 is positioned on a shoulderof end plug 19. A collar 20 is slipped over stud 17 to securely positionend cap 18 against end plug 19. Thereafter, a self-locking nut 16 isthreadably engaged with stud 17 and firmly attaches and coaxially fixesthe unsecured or free end of inner vertical tube 2 to the mutuallyadjacent end of outer guide tube 10. Since the opposite end of innertube 2 is rigidly fastened to support 1 through mounting block 31 andend fitting 62, and since outer guide tube 10 is of a sufiicient axiallength, the outer guide tube 10 is held in compression against support1, thereby causing inner guide tube 2 to remain in tension between thefree end of outer guide tube 10 and support I. The outer guide tube 10is held in compression against support 1 because the lower edge 54 ofouter guide tube 10 is pressed dOwnward into a nylon damping ring 35which, though having vibration damping characteristics, is rigid enoughto support outer guide tube 10 in compression.

The plurality of reed switches S1 through S6 are connected in parallelby common terminals and are longitudinally aligned at predeterminedintervals within inner tube 2. The alignment is not necessarily axial,but is generally longitudinal with respect to the axis of the inner tube2. The plurality of electrical resistors R1 through R6 are connected inseries with each other to form a string of resistors having a first end51 and a second end 40. The string of resistors forms one of the commonterminals of the reed switches with each of the resistors R1 through R6connected between two adjacent reed switches. The string or series ofresistors terminates in a connection wire 27 at junction or first end51, and at a junction or second end 40. A portion of connection wire 27is depicted as being broken off throughout the length of the inner tube2 in FIG. 1 for the sake of clarity. The actual electrical connectionsare more clearly shown in the schematic diagram of FIG. 2. As can beseen by reference to FIG. 2, each reed switch is connected in parallelbetween two common terminals, one of which leads to connection wire 26and the other of which is formed by the resistors R1 through R6 andleads to connection wire 27. Each of the resistors R1 through R6 isconnected between two adjacent reed switches. Resistor R1 is connectedbetween switches S1 and S2 at junctions 40 and 41, resistor R2 isconnected between switches S2 and S3 at junctions 41 and 44, resistor R3is connected between switches S3 and S4 at junctions 44 and 45, and soforth.

Float 5 is a buoyant annular body containing a magnetic element, whichin its preferred form is comprised of two inclined bar magnets 6 and 6of equal length. Bar magnet 6 has a first end 8 and a second end 9 whilebar magnet 6' has a first end 8' and a second end 9. The first ends 8and 8' of the bar magnets lie in the lower portion 59 of float 5 whilethe second ends 9 and 9' of the bar magnets lie in the upper portion 58of float 5. The bar magnets 6 and 6' each lie in separate planesparallel to each other and to the axis Y of the inner tube 2, as can beseen by reference to FIG. 4. The first ends 8 and 8', of bar magnets 6and 6' respectively, lie at the intersections with the respectiveseparate parallel planes containing magnets 6 and 6', of an imaginaryline 2 passing through the'common axis Y of the float 5 and the innertube 2 perpendicular to the respective parallel planes. Each of the barmagnets 6 and 6 diverges from its first end toward its second end at thesame angle 6, and the bar magnets lie in opposite directions from aprojection of the axis Y onto the separate parallel planes containingthe bar magnets 6 and 6'. From FIGS. 3 and 4, it can be seen that thebar magnets 6 and 6 are in a skew relationship with each other. It canalso be seen that the first ends 8 and 8' of the bar magnets are thelower ends and that the second ends 9 and 9' are the upper ends and thatthe angle 0 is about 35. The float 5 could be inverted so that the firstends 8 and 8' would be the upper ends of the bar magnets and the secondends 9 and 9 would be the lower ends. The liquid level 9 indicatorsystem performs equally well using either configuratron.

The result of the configuration of the bar magnets 6 and 6' asillustrated in the drawings is that the magnetic element of the floatsets up an unsymmetrical magnetic field. That is, the magnetic field ofthe magnetic element is stronger toward one end of the inner verticaltube 2 than toward the other end of the inner vertical tube 2. With thefloat 5 in the position indicated, the magnetic field is stronger towardthe lower end of the tube 2 than toward the upper end as measured at theaxis Y. As a result of the unsymmetrical magnetic field, each of thereed switches has but two contact points or planes. That is, each switchwill remain open until the center of float 5 approaches to within agiven axial distance. At that point, the switch will close and remainclosed until the float moves past the switch a different predetermineddistance. For example, the switch S5 of FIG. 1 has an upper contactpoint X and a lower contact point W. It should be noted that because ofthe unsymmetrical magnetic field of float 5, and because the magneticfield of the bar magnets 6 and 6 is stronger toward the lower end ofinner tube 2 than toward the upper end of inner tube 2, the lowercontact point W is more distant from the center of reed switch S5 thanis the upper contact point X. One feature of the magnetic element of thefloat 5 is that it is positioned partially in the upper portion 58 ofthe float 5 and partially in the lower portion 59 of float 5, and upperportion 58 and lower portion 59 may be considered to be of approximatelyequal thickness. The moment of inertia of the part of the magneticelement in the upper portion 58 of the float about the axis Y of theinner tube 2 is larger than the moment of inertia of the part of themagnetic element in the lower portion 59 of the float 5. The part of themagnetic element in the lower portion 59 of the float 5 is comprised ofthose portions of bar magnets 6 and 6' terminating in lower ends 8 and8. It is the essential feature of a difference in moments of inertiathat causes the magnetic field to be unsymmetrical and stronger towardone end of the inner tube 2 than toward the other end. This feature ismost clearly illustrated in FIGS. 5 and 6. FIG. 5 is a sectional view ofthe float 5 taken through the upper portion 58 of float 5. It can beseen that the area of the magnetic element is comprised of the ovalcross-sections of bar magnets 6 and 6', each cross-section being adistance R from the axis Y of the tube 2. The moment of inertia of themagnetic element about the axis Y may thereby be represented by theequation: 1,, (areagl-area R where 1 is the moment of inertia of themagnetic element in the plane of FIG. 5 and area and area, are thehorizontal cross-sectional areas of the bar magnets 6 and 6'respectively. By comparison, the moment of inertia of the magneticelement about the axis Y computed in the plane of FIG. 6 through thelower portion 59 of float 5 may be represented by the equation: 1,,(area,,+area 1 where I is the moment of inertia of the magnetic elementin the plane of FIG. 6 and where the crosssectional area of the barmagnets 6 and 6' are each located a distance r from the axis Y in FIG.6. Since the distance R is greater than the distance r, I, is greaterthan I It can be seen that by integrating the moment of inertia withrespect to the thickness of float 5, the moment of inertia of themagnetic element about the axis Y in the upper portion 58 of the float 5is larger than the moment of inertia of the magnetic element about theaxis Y in the lower portion 59 of the float 5 because the bar magnets 6and 6' are always more distant from the axis Y in the upper portion 58than in the lower portion 59. The magnetic field at the axis Y of tube 2is necessarily greater at the lower extremity of the float 5 than at theupper extremity of the float 5.

A scavenger magnet 30 is fastened to the interior wall of outer guidetube 10. Scavenger magnet 30 is a ring magnet that extends around theinner diameter of outer guide tube 10 and is positioned verticallybetween the lower float position 36 and the lower extremities of thelower flow ducts ll. Scavenger magnet 30 is positioned laterally betweenthe inner tube 2 and the outer tube 10. As a result of the magneticcharacteristics and positioning of scavenger magnet 30, magnetizableparticles carried in the liquid within which transmitter 60 ispositioned are disentrained from the liquid and trapped by scavengermagnet 30 as liquid-passes from the exterior of outer guide tube 10through lower flow ducts 11 and into the enclosure 13 between the innertube 2 and the outer guide tube 10. Stray metallic particles are therebyremoved from the tank and do not interfere with or distort the operationof the reed switches.

Float 5 is constructed of an annular ring of buoyant plastic to theinterior surface of which an inner annular nylon guide [4 is fastened toinsure smooth dependable vertical movement of the float 5 with respectto inner tube 2 between the upper position, in which it is depicted inFIG. 1, and the lower float position designated as 36. The float 5floats at the liquid level present in the liquid storage tank in whichthe transmitter 60 is located. The bar magnets 6 and 6' provide amagnetic field that operates the reed switches when the float passes theswitch contact points. This results in a progressive switch closure asthe float moves axially along the inner tube 2. As the float 5 risesfrom the lower float position 36, progressive switch closure occurs andthe resistors R1 through R6 are sequentially shorted out of the reedswitch circuit. As shown in the electrical schematic of FIG. 2, theshort circuiting of resistors R1 through R6 reduces the overallresistance in the reed switch circuit between contact pins A and B. Ineffect, the resistance measured between pins A and B is an inverseanalog of the float position and, in turn, of the liquid level. Aresistor 38 having a substantial resistance, though not an essentialelement of the invention, always remains in the reed switch circuit as aprotective resistor. When the float 5 is in the lower float position 36,reed switch S1 is closed and the circuit path is closed throughconnecting wire 26, protective resistor 38, junction 39, switch S1,junction 40, and through every resistor R1 through R6 and back throughconnecting wire 27 to contact pin A. As the float 5 rises from thelowest float position 36, the switch S2 is subjected to the magneticfield of bar magnets 6 and 6'. This causes switch S2 to close therebyshort circuiting resistor R1. The electrical path between contact pins Band A is through connecting wire 26, protective resistor 38, junction42, switch S2, junction 41, and resistors R2 through R6 and back to pinA through connecting wire 27. Because of the configuration of barmagnets 6 and 6' the magnetic field at the axis of inner tube 2 isstronger in a downward direction from float 5 than in an upwarddirection from float 5. The switch S1 thereby remains closed until float5 rises about even with switch S2, at which time switch S1 is beyond theinfluence of the magnetic field and therefore returns to an opencondition. As float 5 rises still further, switch S3 is closed therebyshort circuiting both of the resistors R1 and R2. The electrical pathbetween contact pins B and A is then through connecting wire 26,protective resistor 38, junction 43, switch S3, junction 44, andresistors R3 through R6, then through connecting wire 27 back to pin A.The sequential short circuiting of resistors continues as float 5 risesuntil all of the resistors R1 through R6 are short circuited when thefloat 5 is in the upper float position. At this point, the electricalcircuit between contact pins B and A is through connecting wire 26,protective resistor 38, junction 52, switch S7, junction 51, and backthrough connecting wire 27 to pin A. From the operation of thetransmitter 60, it can be seen that each of the resistors R1 through R6has a control switch associated therewith. That is, one of the two reedswitches adjacent to each resistor controls the presence in the circuitof that resistor. Switch S2 is the control switch for resistor R1,switch S3 is the control switch for R2, and so forth.

In the progressive short circuiting of resistors R1 through R6, eachadditional resistor short circuited produces a corresponding decrease inthe total resistance in the reed switch circuit between pins B and A anda corresponding increase in current through the circuit. If the liquidstorage tank is oddly shaped, the resistors R1 through R6 will be chosenso that the resistance value of the resistors located between adjacentreed switches varies in proportion to the horizontal cross-sectionalarea of the tank at the vertical level of the control switch as sociatedwith each of the resistors. For example, if the tank has a smallcross-sectional area at the top of the tank, a large cross-sectionalarea at the center of the tank, and a small cross-sectional area at thebottom of the tank, the electrical resistances of the various resistorswill differ accordingly. That is, the resistors R5 and R6 and theresistors R1 and R2 will be relatively small as compared with resistorsR3 and R4. This will reflect a smaller change in current as the float 5moves in the upper or lower portion of the tank as compared with themovement of the float in the central portion of the tank. This willaccurately reflect the relative change in volume, since a movement ofthe float a given distance in the upper or lower portion of the tankwill result from a proportionately smaller change in volume than anequal linear movement of the float in the central portion of the tank.

in FIG. 2 it can be seen that the indicator system 7 is connected to thecommon terminals of the reed switch circuit through connecting wires 26and 27 and provides a constant input voltage to the reed switches 81through S7 and the resistors Rl through R6 display the output voltagefrom the switches and resistors as determined by the axial location ofthe float with respect to the inner vertical tube 2. The electricalconfiguration of the indicator system 7 is shown in FIG. 2. Theelectrical current for the operation of the liquid level indicatorsystem is supplied to indicatorsystem from electric lead 29. The powerfor the operation of the liquid level indicator system is supplied onlead 29 through pins E to a constant current regulator 53. Constantcurrent regulator 53 is comprised of a resistor temperature compensatedreference diode circuit and is designed to protect the rest of thecircuitry of the liquid level indicator system from large voltagesurges. The output of constant current regulator 53 is connected throughfixed resistors 55 and 56 and adjustable resistor 57 to a currentindicator means which is illustrated as a milliameter 58. A blockingdiode 70 is connected to ground between the resistors 55 and 56.Blocking diode 70 will not pass a current up to a predetermined voltage,such as 5 volts. Current produced from all voltage over thispredetermined voltage is passed through blocking diode 70 to ground. Asa result, as long as the input voltage on lead 29 is kept above thispredetermined voltage, the predetermined voltage will be applied toresistor 56 and all subsequent impedances in the circuit. Anyfluctuations in voltage will merely be conducted to ground throughblocking diode 70. The voltage passing through milliameter 58 andthrough the reed switch circuit is therefore highly stable. Milliameter58 is the visual display device and is calibrated in terms of depth orvolume of liquid within the storage tank. The current from thepredetermined voltage flows through resistor 56, resistor 57,milliameter 58, and contact pins D to connecting wire 26 and then to thecontact pins B of the transmitter 60. Within transmitter 60 the currentflows through resister 38 and none, some, or all of the resistors Rlthrough R6 as previously described and back to contact pins A. Fromcontact pins A the current flows from the transmitter 60 back to thepins J of indicator system 7. From pins J the current is conducted toground through pins F. As the resistance within the transmitter 60varies with the liquid level, the current flowing through themilliameter 58 varies proportionately. Electric lead 28 of the indicatorsystem 7 is used to supply a small voltage for an interior lamp 4 withinthe indicator system 7. The current for the operation of the lamp isconnected to the indicator system 7 through pins G, and the lamp 4 isgrounded through pins H.

The two portions of the electrical contacts comprised of the pins E, F,G, H, D, and J are each comprised of a plug-in type electrical interfacefor easy attachment to and detachment from the indicator system 7.Similarly, the pins A and B are of the plug-in type variety, and contactwith the transmitter 60 may easily be made or broken. Indicator system 7may easily be used with any other transmitter having differentresistance values by recalibrating the indicator system 7 by merelyvarying the adjustable resistor 57.

The schematic wiring diagram for a modified form of the liquid levelindicator system is illustrated in FIG. 7. At transmitter 60', a pin Cis inserted between pins A and B. At indicator system 7', a pin I isinserted between pins D and J. These additional pins enable anadditional electrical connection, to be made between the transmitter 60'and the indicator system 7'. A ratio meter 71 is substituted in theindicator 7 in place of the resistors 55, 56, and 57, the blocking diode70, the constant current regulator 53 and the milliameter 58 in FIG. 2.Resistor 38 is removed from the transmitter 60 to facilitate ratioreadings. Ratio meter 71 has a first coil 72 and a second coil 73, eachcoil having a common terminal 74 and separate terminals as illustrated.Lead 29' may be considered to be a first electric power lead while lead75 may be considered to be a second electric power lead. The power forthe operation of the liquid level indicator system is supplied on lead29' through pins E and J. Lead 29' is connected to the first end 51 ofthe resistor string in transmitter 60' through wire 27 and pins J and A.The separate terminal of the second coil 73 of ratio meter 71 isconnected to the reed switches by wire 26 through pins D and B. Thesecond electric power lead 75 is connected to the common terminal 74 ofcoils 72 and 73 and to ground at pins F. The separate terminal of thefirst coil 72 is connected to the second end or junction 40 of theresistor string in transmitter 60' by wire 76 which passes through pinsl and C.

The wiring arrangement of FIG. 7 has some advantage over that of FIG. 2in that the ratio meter 71 uses two coils instead of the single coilemployed in milliameter 58. All of the resistances RI through R6 areconnected in series with the first coil 72 while the coil 73 isconnected in series with some, none, or all of the resistors Rl throughR6. That is, as the float 5 ascends along the inner tube 2, the coil 73is connected in series with more and more of the resistances R1 throughR6. The converse is true as the float descends. The ratio meter 71senses the ratio of the resistances connected to coil 73 to the fullresistance load connected to coil 72; This ratio is reflected in thecalibrated reading of the ratio meter 71. it can be seen that as theswitches 81 through S7 progressively close, the ratio changesaccordingly. The advantage of this type of circuitry is that no voltagestabilization is required on the first power lead 29', because anyvoltage change affects both of the coils 72 and 73 but does not affectthe ratio.

Once again referring to FIG. I, it can be seen that the transmitter 60has a long length in comparison to its diameter. One serious problemwith conventional liquid level indicator systems utilizing long tubes isthe problem of resonant vibration. A rigid tube will frequently achieveresonant vibration and fail rapidly when subjected to externalvibration, so that some type of damping is required. In the structure oftransmitter 60 the outer tube 10 and the inner tube 2 are firmlyattached to each other at their mutually adjacent upper ends remote fromthe support 1. The lower end of inner vertical tube 2 is rigidly mountedon support 1 through end fitting 62 and mounting block 31. The innertube 2 will therefore tend to resonant when support 1 is subjected toexternal vibration. In order for tube 2 to vibrate, it is necessary forthe outer tube 10 to also vibrate. As soon as the outer tube 10 startsto move, however, its lower edge 54 moves with respect to the damperring 35. That is, the lower edge 54 of outer tube 10 lifts up from oneside of damper ring 35 and further compresses on the other side ofdamper ring 35. The opposing variable forces which the damper ring 35exerts on the outer guide tube 10 change the overall forces acting onthe outer guide tube I0 and the inner tube 2 and prevent a resonantcondition from developing in the transmitter 60. If resonance cannotoccur or be maintained in the inner tube 2 or the outer tube 10, thevibration amplitudes imposed on the transmitter 60 do not create stressproblems. The design feature of rigidly fastening the adjacent ends ofthe inner and outer tubes and fastening the inner tube to the support 1so that the outer tube is in compression while the inner tube is intension makes variable a resonance frequency that would otherwise beconstant, and so prevents the free end of transmitter 60 from achievinglateral resonant oscillation.

While the transmitter 60, as illustrated in the drawings is shown asbeing mounted to the floor of a liquid storage tank, it performs equallyas well when vertically mounted upon any support within the liquidstorage area, and may be mounted from an overhead support so that thefree end of the inner tube 2 extends downward. In such a case slight,inconsequential circuit modifications would have to be made in order forthe current indicator means employed to reflect measurements identicalto those obtained with the embodiment of FIG. 1 for corresponding liquidlevel conditions.

The foregoing detailed descriptions and illustrations of severalembodiments of this invention have been given for cleamess ofunderstanding only, and no unnecessary limita tions should be construedtherefrom, as other modifications will be obvious to those familiar withliquid level indicator systems.

We claim as our invention:

l. A liquid level indicator system comprising:

a. a hermetically sealed vertical tube of uniform cross sec tionconstructed of a non-magnetic material;

b. a plurality of-reed switches connected in parallel by commonterminals and longitudinally aligned within said tube;

0. a plurality of electrical resistors connected in series with eachother to form one of the aforesaid common terminals with each of saidresistors connected between two adjacent reed switches;

d. a float carrying a magnetic element positioned co-axially about saidtube and vertically movable with respect to said tube between an upperand a lower float position, said magnetic element comprising twoinclined bar magnets of equal length each having first and second endsand each lying in separate planes parallel to each other and to the axisof said tube, said first ends of said bar magnets lying at theintersections of said separate planes with a line that passes throughthe axis of said tube perpendicular to said separate planes, each ofsaid bar magnets diverging from its first end toward its second end atthe same angle and in opposite directions from a projection of the axisof said inner tube onto said separate parallel planes, whereby said barmagnets are in a skew relationship with respect to each other; and,

e. an indicator system connected to said common terminals for providingan input voltage to the aforesaid switches and resistors and forregistering the current passing through said switches and resistors asdetermined by the longitudinal location of said float with respect tosaid vertical tube.

2. The liquid level indicator system of claim 1 further comprising asupport, an outer guide tube positioned radially exteriorally from saidfloat and co-axial with respect to said vertical tube thereby forming anenclosure between said vertical tube and outer guide tube, upper andlower flow ducts connecting said enclosure to the exterior of said outertube, and said vertical tube and outer guide tube are firmly attached toeach other at mutually adjacent ends, and the end opposite the mutuallyadjacent end of said vertical tube is rigidly fastened to said supportand said outer tube is held in compression against said support by saidvertical tube, thereby causing said inner tube to remain in tension.

3. The liquid level indicator system of claim 1 further characterized inthat an outer guide tube is positioned radially exteriorally from saidfloat and co-axial with respect to said vertical tube thereby forming anenclosure between said vertical tube and outer guide tube, upper flowducts and lower flow ducts located below said lower float positionconnecting said enclosure to the exterior of said outer tube, and ascavenger magnet positioned between said float and said lower flowducts, whereby magnetizable particles carried in liquid are disentrainedand trapped by said scavenger magnet as liquid passes through said lowerflow ducts.

4. The liquid level indicator system of claim I further characterized inthat said magnetic element creates an unsymmetrical magnetic field.

5. The liquid level indicator system of claim I further characterized inthat said first ends are lower ends and said second ends are upper endsof said bar magnets, and said angle is about 35.

6. The liquid level indicator system of claim I further comprising asupport, and wherein said tube is mounted on said support in a tankcontaining liquid, and said electrical resistors are each shortcircuited by operation of a control switch which is one of said adjacentreed switches between which said resistors are connected, and theresistance value of the resistors located between adjacent reed switchesvaries in proportion to the horizontal cross-sectional area of said tankat the vertical level of the control switch associated with saidresistors.

7. In a liquid level indicating system having an hermetically sealedvertical tube containing a reed switch circuit and having first andsecond ends and mounted in a tank containing a liquid, a liquid leveldisplay device electrically connected to said reed switch circuit afloat having upper and lower portrons carrying a magnetic element andpositioned co-axrally about said tube and vertically movable withrespect to said tube between an upper and lower float position, saidmagnetic element being comprised of two inclined bar magnets of equallength each having first and second ends and each lying in separateplanes parallel to each other and to the axis of said tube, said firstends of said bar magnets lying in one of said upper and lower portionsof said float at the intersections with said separate planes of a linethrough the axis of said tube perpendicular to said separate parallelplanes, and said second ends of said bar magnets lying in the other ofsaid upper and lower portions of said float, each of said bar magnetsdiverging from its first end toward its second end at the same angle andin opposite directions from a projection of the axis of said tube ontoeach of said separate parallel planes, whereby said bar magnets are in askew relationship with respect to each other, said magnetic elementpartially in said upper portion and partially in said lower portion ofsaid float, and said magnetic element having the moment of inertia aboutthe axis of said tube of the part of said magnetic element in one ofsaid portions of said float larger than the moment of inertia of thepart of said magnetic element in the other of said portions of saidfloat, whereby the magnetic field of said magnetic element is strongertoward one of said first and second ends than toward the other of saidfirst and second ends of said vertical tube.

8. The liquid level indicator system of claim 7 further characterized inthat said first ends of said bar magnets lie in said lower portion ofsaid float and said second ends of said bar magnets lie in said upperportion of said float, and said angle is about 35.

1. A liquid level indicator system comprising: a. a hermetically sealedvertical tube of uniform cross section constructed of a non-magneticmaterial; b. a plurality of reed switches connected in parallel bycommon terminals and longitudinally aligned within said tube; c. aplurality of electrical resistors connected in series with each other toform one of the aforesaid common terminals with each of said resistorsconnected between two adjacent reed switches; d. a float carrying amagnetic element positioned co-axially about said tube and verticallymovable with respect to said tube between an upper and a lower floatposition, said magnetic element comprising two inclined bar magnets ofequal length each having first and second ends and each lying inseparate planes parallel to each other and to the axis of said tube,said first ends of said bar magnets lying at the intersections of saidseparate planes with a line that passes through the axis of said tubeperpendicular to said separate planes, each of said bar magnetsdiverging from its first end toward its second end at the same angle andin opposite directions from a projection of the axis of said inner tubeonto said separate parallel planes, whereby said bar magnets are in askew relationship with respect to each other; and, e. an indicatorsystem connected to said common terminals for providing an input voltageto the aforesaid switches and resistors and for registering the currentpassing through said switches and resistors as determined by thelongitudinal location of said float with respect to said vertical tube.2. The liquid level indicator system of claim 1 further comprising asupport, an outer guide tube positioned radially exteriorally from saidfloat and co-axial with respect to said vertical tube thereby forming anenclosure between said vertical tube and outer guide tube, upper andlower flow ducts connecting said enclosure to the exterior of said outertube, and said vertical tube and outer guide tUbe are firmly attached toeach other at mutually adjacent ends, and the end opposite the mutuallyadjacent end of said vertical tube is rigidly fastened to said supportand said outer tube is held in compression against said support by saidvertical tube, thereby causing said inner tube to remain in tension. 3.The liquid level indicator system of claim 1 further characterized inthat an outer guide tube is positioned radially exteriorally from saidfloat and co-axial with respect to said vertical tube thereby forming anenclosure between said vertical tube and outer guide tube, upper flowducts and lower flow ducts located below said lower float positionconnecting said enclosure to the exterior of said outer tube, and ascavenger magnet positioned between said float and said lower flowducts, whereby magnetizable particles carried in liquid are disentrainedand trapped by said scavenger magnet as liquid passes through said lowerflow ducts.
 4. The liquid level indicator system of claim 1 furthercharacterized in that said magnetic element creates an unsymmetricalmagnetic field.
 5. The liquid level indicator system of claim 1 furthercharacterized in that said first ends are lower ends and said secondends are upper ends of said bar magnets, and said angle is about 35*. 6.The liquid level indicator system of claim 1 further comprising asupport, and wherein said tube is mounted on said support in a tankcontaining liquid, and said electrical resistors are each shortcircuited by operation of a control switch which is one of said adjacentreed switches between which said resistors are connected, and theresistance value of the resistors located between adjacent reed switchesvaries in proportion to the horizontal cross-sectional area of said tankat the vertical level of the control switch associated with saidresistors.
 7. In a liquid level indicating system having an hermeticallysealed vertical tube containing a reed switch circuit and having firstand second ends and mounted in a tank containing a liquid, a liquidlevel display device electrically connected to said reed switch circuit,a float having upper and lower portions carrying a magnetic element andpositioned co-axially about said tube and vertically movable withrespect to said tube between an upper and lower float position, saidmagnetic element being comprised of two inclined bar magnets of equallength each having first and second ends and each lying in separateplanes parallel to each other and to the axis of said tube, said firstends of said bar magnets lying in one of said upper and lower portionsof said float at the intersections with said separate planes of a linethrough the axis of said tube perpendicular to said separate parallelplanes, and said second ends of said bar magnets lying in the other ofsaid upper and lower portions of said float, each of said bar magnetsdiverging from its first end toward its second end at the same angle andin opposite directions from a projection of the axis of said tube ontoeach of said separate parallel planes, whereby said bar magnets are in askew relationship with respect to each other, said magnetic elementpartially in said upper portion and partially in said lower portion ofsaid float, and said magnetic element having the moment of inertia aboutthe axis of said tube of the part of said magnetic element in one ofsaid portions of said float larger than the moment of inertia of thepart of said magnetic element in the other of said portions of saidfloat, whereby the magnetic field of said magnetic element is strongertoward one of said first and second ends than toward the other of saidfirst and second ends of said vertical tube.
 8. The liquid levelindicator system of claim 7 further characterized in that said firstends of said bar magnets lie in said lower portion of said float andsaid second ends of said bar magnets lie in said upper portion of saidfloat, and said angle is about 35*.